YAOPT: Yet another oil pressure thread. :)

MysticLlama · 06-18-2004, 07:20 PM

I've been searching through the archives, but I haven't yet found anything that's quite like this situation. I may be overreacting, but I was party to a VW Cabriolet one time that was the spawn of the devil, so oil issues make me twitchy.

It was one of the warmest days of the year in Seattle today, 86 degrees (okay, all the Texans and SoCal people can chuckle now) and so the car was running a little warmer than normal.

Normally I don't see it ever above the top of the white box, when I drove it up from Southern Oregon on a several hour trip it was maybe up a millimeter or so, about the same when I drove up a 5 mile hill test driving it.

So today I get stuck in traffic and it goes a little higher, still not anywhere near the halfway mark between the box and the red zone, maybe not even 1/3rd actually.

The thing that was bugging me though was pressure. Once it warmed up it wasn't wanting to go much above 2bar at cruising speed (about 3000 in 5th) and when revving to 5k or so from a couple of stoplights, it only made it to 3.

Seems a little low, as I've been driving it near every day for about 3 weeks since I got it, and it's usually the 1bar per 1000 ratio. It also settles in at about .2-.3 when at idle vs. the normal .8-1.

I checked the oil while it was warm when I got home, and it was right at the full mark. This thing doesn't drip, and it seems to burn hardly anything. Is that weird?

So I cleaned the connections on what I think is the oil sending unit (as well as the other few right there on top just to be sure) and I want to run it for a ride again, but I also don't want to blow something up.

So..... am I just paranoid? What do I need to check?

Btw, the temp didn't go up once it levelled out during the drive home, which is about 30 minutes. It didn't continue to go up, just got to it's little higher than normal and quit. Doesn't seem to be a temp problem, I'm more concerned about pressure.

MysticLlama · 06-18-2004, 07:54 PM

Oops, I should know this by now...

1980 SC 3.0

Jim Sims · 06-18-2004, 11:08 PM

What weight and type of oil are you using? Jim

MysticLlama · 06-18-2004, 11:12 PM

I'm pretty sure it's 20-50w as put in by the PO. He even gave me a couple extra bottles to throw in the trunk for the trip and that's what they were.

Edit: It's Castrol if the spares are any indication.

Kurt B · 06-19-2004, 05:09 AM

You know, my oil pressure is really low on the 84. Now I have a comparison with the 964. If they are supposed to read the same way, then something is nasty wrong.
The bar reads at the very most, I think 2.5 or maybe three when the rpms are at 5000. When I'm idling it's below zero.
I've tried checking the connection back in the engine bay, but aside from getting it working (which it didn't when I got the car), no difference.
Been this way since I got the car in 99 at 123k miles. It has 201,000.
It may just be that you can drive a crippled 3.2 for 70k miles and tear up the joint, I don't know, but you gotta also wonder about the mechanics of getting that reading. The sender, the connection?

Doug Zielke · 06-19-2004, 07:26 AM

The only way to really know what's going on, is to plumb in a *mechanical* guage that's known to be accurate.
A healthy 911 motor should see 1bar per 1000 rpm.

MysticLlama · 06-19-2004, 11:09 AM

Well, I got outside and messed with it a bit today, and even cold it won't go much above 3, 3.5 if I really mash on it for a sec, but then it starts to sound a little grouchy, which it never has before, so I probably shouldn't drive it much if at all.

This seemed to happen all at once, not a gradual thing. When it's a bearing problem, doesn't it happen by wearing down?

I read a couple of other bits in threads about some valves possibly being stuck closed?

How can I find and test those?

klaucke · 06-19-2004, 12:03 PM

Just for reference, when your oil temps are higher, your oil pressures will be lower. I notice when my oil temp gets up at about 210ish, only on the hottest days, that the oil pressure is lower than normal, and I'm running 20w-50.

In your case the difference could be drastic enough as not to attribute it solely to increased oil temp.

Not to rob the thread, but what is a too high a temp? 210? 200?

Porsche_monkey · 06-19-2004, 12:08 PM

1. Other than the oil squirters, what you really need is flow, not pressure. Yes, from your numbers, your pressure is low.

2. What are you goning to do about it? I would suggest drive it. Some day it will fail. When it does, fix it.

3. I believe Bruce A says '225 is hot 250 way too hot'. Perhaps someone can confirm this.

MysticLlama · 06-19-2004, 12:28 PM

Well, if I can drive it until it fails without it costing me anymore than it would to fix it in advance, I would. That's the part I'm mainly worried about.

If something bad happened that could cost $1000-1500 to fix, that would hurt, and it'd take me a few to save it up, but it's still a lot cheaper than a rebuild.

I worry a little that it sounded a little dry in the upper range, but that was just free revving it pretty cold in the garage, which I've never done, so I don't have much to compare to really, maybe it's always done that.

The temps didn't seem too bad really, not much more than what I would expect from the weather anyway.

I guess my big worry is that it really seems like it "sticks" at 3-3.5 bar, almost like a blockage or something.

I'll drive it around (nicely) in a little bit and see how it acts, I'll just stay within 100 miles of home so AAA can get me back.

soup dragon · 06-19-2004, 01:37 PM

If it was my car i would try the cheapest fix first.
Replace the oil and filter and see if that improves things.

singpilot · 06-19-2004, 02:50 PM

Which cooler? Standard trombone?

My '80SC runs 1bar to 1K RPM MORE OR LESS until the oil gets above 200-ish on the temp. Then the 1 to 1 ratio slacks off. When oil temp is 210 or so, at idle, the pressure 'reads' close to zero. I was told go by the light. If that light comes on, shut off, pull over. At ANY time.

Every SC I have seen or driven is in that ball park.

Imagine having one of these with functioning A/C in Las Vegas (summer ambient temps always above 100F). Is why I got the Carrera cooler, aux scoop with the fan. Problem solved for the most part. I also run Castrol 20-50W.

Enjoy.

Kurt B · 06-19-2004, 02:56 PM

Your car is not going to completely quit from low oil pressure, believe me. It may take its toll in the long run of course. You may want to have pro check it out. Someone who's not out to scare you out of your money and will give you an honest assessment like John Walker who's up in Washington somewhere (john walker's workshop is his handle)! He's got a shop in WA and posts here. I called him one Saturday morning when I thought I trashed my tranny and was freaked, and he helped me over the phone, and with his help, I discovered it was the outer right CV joint, and I was able to replace it that day.

MysticLlama · 06-19-2004, 03:10 PM

It's the standard trombone cooler, yeah.

It is looking close to 0 at idle when warm, and it sounds like maybe it's in the ballpark.

I can't rely on the light though unfortunately. During the chain tensioner upgrade the PO did, the green oil light and parking brake light got broken/shorted together, so they stay on and flicker together.

The work done on that invoice was:
Replaced Timing Chain tensioners, installed tensioner oil lines
R/R engine resealed oil cooler
Reroute hose
Removed broken studs on right exhause heater box, installed ?? (can't read it)
Replaced exhaust cat pipe

After that stuff was done, the oil and brake light are stuck on and flicker together, and the speedometer doesn't work anymore. I'm really not sure what I'm looking at when I'm looking at it, so I don't know where to start looking for the oil light/brake light short.

MysticLlama · 06-19-2004, 03:12 PM

And I am going to take it to John, for a tranny fluid change, and an overall look it over and get a list of what he would do, in what order, I just have been really slammed with work and have to get the times scheduled right, it's fairly close to home, but a long ways from the office.

singpilot · 06-19-2004, 03:29 PM

Wow, I consider that oil pressure light a no-go item. As is the Alternator (belt fail) light. Both of these should be checked EVERY start-up. Some people put a buzzer on both.

I would DEFINATELY have him fix the oil light. He can verify the oil pressure then too.

johnsjmc · 06-19-2004, 03:37 PM

You can also consider installing the "964 cam oil line restrictors" They brought my hot pressure up 1 bar in a 1980 SC. Cost about $30

rob911 · rob911's Garage

I have similar pressures, although I can get 4+ bar even on a hot engine if I am really "driving" - using revs up to redline.
Idle pressure is bouncing off the bottom when warm, just watch for oil and alternator warn lamps.
Guess after 175,000 miles things aint as tight as they once were. So long as the oil keeps going round and the temperature stays below the middle I will just keep donig it to it.
Does everyone else use all 6200rpm in a a high-ish mile engine?

WERK I · WERK I's Garage

The thing that is important in any engine is the volume of oil flow to lubricate, not the oil pressure in which it is under(to a degree of course). Since there is not an accurate/inexensive method in which to measure oil volume of flow in today's engines, the oil pressure method is a reliable one.
MysticLlama, since you note you are not burning any oil. It is safe to assume the top-end(valve guides and piston rings) is in very good condition. The biggest thing that "bleeds-off" oil pressure on a high mileage engine are the crank mains and rod journals. As an engine wears the clearances in the journals increase and thereby increasing the oil flow to these areas. With the increased flow in these areas, you will see a pressure drop in the entire oil circuit. The 964 oil restrictors will bump the oil pressure, but it only masks the symptom. I don't know why, but a lot of SC's I have looked at seem to show lower pressures than most of Carreras of same mileage. Maybe they used softer bearing materials back then? The 3.0l is a damn near bullet proof engine, going well over 200K miles more often than not, before a teardown. The oil pump is another possibility, but I hear it is a pretty good unit. It just may not have the reserve capacity of turbo or 964 pumps. Remember, Porsche even states that the oil pressure light may even come on at idle. I believe the light trips on in the 5-10psi range.
I wouldn't sweat the oil pressure for now. Just keep listening for any "unusual" knocking sounds at idle.

turbocarrera · 07-08-2004, 03:43 PM

I feel a little better reading this thread. I've got 114k miles on mine and I barely get over 3 bar when cold and not over 2 when hot - makes me think I'm going to need a complete rebuild sooner than later. I thought it might be because I have a few consistent leaks, as well as my fairly high mileage. That said, it never gets hot, burns about a litre every 1000miles, great power, smooth - runs like a champ. I had it @6k rpm in 4th for 5 minutes once with no ill effects that I know of. So I guess I'll just keep wringing it's filthy little neck till it either wrings me back, or I rebuild it.